•A real-scale vegetal façade was monitored during three years in a Mediterranean climate.•Results show that the vegetation layer improves interior environmental conditions.•A predictive numerical model was fitted and experimentally validated.•Results show the high accuracy of the model, being the R-squared around 85%.•The model is suitable for buildings located in similar climates to the one studied. This article presents the results of an experimental study carried out in a vegetal façade situated in a locality close to Madrid. The objectives of the study are to develop a performance predictive model of a vegetal façade whose independent variables are irradiance, exterior temperature and relative humidity, based on the effect of the vegetation on the environmental conditions of the building, as well as to characterize thermally the vegetal element by comparing two identical enclosures (with a vegetal layer present in one of them being the only difference). The results of the three-year monitoring period are analyzed by means of statistical data processing and an autoregressive model is fitted. This model estimates the temperature difference between both enclosures. The validation of the model based on the experimental data is done subsequently. Once the improvements caused by the vegetation on the interior environmental conditions of the building have been quantified, the results show that it is possible to predict with high accuracy the vegetation's performance, being the multiple R-squared of the estimated models around 85%. Furthermore, the application of the model is suitable for other buildings located in a similar climate to the one studied, as the independent variables exclusively depend on climate conditions.